The rapidly evolving field of bioengineering has created a demand for a diverse library of different types of polymers offering a wide variety of choice of physical, mechanical, chemical and physiological properties. It is desirable that libraries of many different materials be available so that the specific polymer properties can be optimally matched with the requirements of the specific applications under development.
Examples of polymers suitable for various bioengineering applications include those described in U.S. Pat. Nos. 5,099,060; 5,665,831; 5,916,998 and 6,475,477, along with the polymers described in U.S. Patent Publication Nos. 2006/0024266, 2006/0034769, 2013/0203713 and 2015/0045451. There are numerous applications in which it is considered desirable for an implanted medical device to maintain its integrity and performance characteristics for extended periods of time, even under demanding mechanical conditions such as repeated mechanical flexure.
Although many types of bioresorbable and/or biodegradable polymers are known, in most of these polymers diphenolic monomers are prepared by linking two suitably protected tyrosine molecules or tyrosine analogs via an amide linkage. These amide linkages do not degrade hydrolytically under physiological conditions and therefore the monomers which have low solubility in water, dissolve very slowly. Further, due to hydrogen bonding of amide hydrogen the melt viscosity of the polymers derived from these monomers is very high, which makes thermal processing more difficult. In addition, bioresorbtion and/or biodegradation tend to alter mechanical properties in unpredictable ways that are not necessarily linearly related to each other.
Thus, there is a need for biocompatible polymers having desirable bioresorbability and biodegradability as well as good processibility under thermal conditions. There remains a need for nontoxic polyarylates having a moderate rate of bioerosion, suitable for use as tissue-compatible materials for biomedical uses.